1. Field of the Invention
The present invention relates to an internal combustion engine that includes a NOx adsorber.
2. Background Art
The heavy-duty engine business is extremely competitive. Increasing demands are being placed on engine manufacturers to design and build engines that provide better engine performance, improved reliability, and greater durability while meeting more stringent emission and noise requirements. One approach to meet more stringent emission requirements is to utilize a NOx adsorber. NOx are believed to be an environmental hazard, and are created when combustion temperatures become excessive. NOx are a particular concern in the turbocharged diesel engine.
A NOx adsorber or NOx trap is an aftertreatment device that stores or adsorbs NOx under lean conditions. Periodically, the NOx adsorber must be regenerated in order to continue collecting the NOx emissions. Under rich conditions, the NOx adsorber catalytically reduces the stored NOx. In a typical arrangement for a diesel engine, a post injection of a reductant such as diesel fuel directly into the exhaust gas creates the rich conditions required for NOx adsorber regeneration. In one arrangement, three seconds of regeneration are required for each one minute of NOx adsorber operation.
For good regeneration, it is desired that the fuel (or other injected substance) be well mixed with the exhaust flow before entering the aftertreatment device. To improve the mixing, the current practice is to inject at an elbow, allow a long length of piping after the fuel is injected before entering the aftertreatment device, or a combination of these or other mixing schemes. Further background information may be found in U.S. Pat. Nos. 4,505,106; 6,442,933; 6,523,342; and 4,359,862.
For the foregoing reasons, there is a need to address the issue of mixing the reductant with the exhaust gas before entering the aftertreatment device.